@SeekingSolace the girl bought a massage tool that is two rollers attached to a handle, which you can rub on your face your massage it.
The brother took the massage tool, placed it at his crotch, and used the shape of two circular rollers attached to a handle to declare "hey look it's my dick".
Taking offense to her massage tool being intimated to be her brother's gentials in such a crude way, along with actually putting the tool on his crotch, caused the girl to be aggrieved, and she therefor kicked her brother in the stomach hard enough to draw blood.
I hope this clears things up.